Piezoelectric micro speaker and method of manufacturing the same

Abstract

A piezoelectric micro speaker and a method of manufacturing the same are provided. The piezoelectric micro speaker includes a device plate, a front plate bonded on a front surface of the device plate, and a rear plate bonded on a rear surface of the device plate. The device plate includes a diaphragm, a piezoelectric actuator that vibrates the diaphragm, and a front cavity disposed in front of the diaphragm. The front plate includes a radiation hole connected to the front cavity. The rear plate includes a rear cavity formed in a surface of the rear plate facing the piezoelectric actuator, and a bent hole connected to the rear cavity. A sound absorption layer is formed on an inner surface of the rear cavity and absorbs sound radiated backward from the diaphragm so as to suppress the sound from being reflected on the rear plate.

What is claimed is: 
     
       1. A piezoelectric micro speaker comprising:
 a device plate comprising a diaphragm, a piezoelectric actuator that vibrates the diaphragm, and a front cavity disposed in front of the diaphragm; 
 a front plate which is disposed on a front surface of the device plate, the front plate comprising a radiation hole connected to the front cavity; and 
 a rear plate which is disposed on a rear surface of the device plate, the rear plate comprising: 
 a rear cavity which is formed in a surface of the rear plate facing the piezoelectric actuator, 
 a bent hole which is connected to the rear cavity, 
 a sound absorption layer which is disposed on an inner surface of the rear cavity and absorbs sound radiated backward from the diaphragm, and 
 a wiring layer formed on the surface of the rear plate facing the piezoelectric actuator, 
 wherein the sound absorption layer covers at least a portion of the wiring layer disposed in the rear cavity of the rear plate. 
 
     
     
       2. The piezoelectric micro speaker of  claim 1 , wherein the sound absorption layer is formed of a material having a lower acoustic impedance than that of silicon. 
     
     
       3. The piezoelectric micro speaker of  claim 2 , wherein the sound absorption layer is formed of one selected from the group consisting of a polyurethane foam, a polymer, a rubber, and any mixtures thereof. 
     
     
       4. The piezoelectric micro speaker of  claim 1 , wherein the piezoelectric micro speaker is installed on a printed circuit board, and
 wherein an auxiliary sound absorption layer that absorbs sound passed through the bent hole is formed in a portion of the printed circuit board facing the bent hole. 
 
     
     
       5. The piezoelectric micro speaker of  claim 1 , further comprising:
 a first wiring layer formed on the inner surface of the rear cavity; 
 a second wiring layer formed on a bottom surface of the rear plate; and 
 at least one connection wire connecting the first and second wiring layers via at least one penetrating hole formed in the rear plate. 
 
     
     
       6. The piezoelectric micro speaker of  claim 5 , wherein the sound absorption layer is disposed directly on both the first wiring layer and a portion of the inner surface of the rear cavity not having the first wiring layer formed thereon. 
     
     
       7. The piezoelectric micro speaker of  claim 6 , wherein the device plate is disposed between the front plate and the rear plate so that the front cavity and the rear cavity are axially aligned with the piezoelectric actuator disposed therebetween.